The conventional method of endotracheal intubation involves the insertion of a tubular device (an endotracheal tube) into the trachea. The endotracheal tube continues through the trachea and stops above the carina anterior to a position between the 2.sup.nd and 4.sup.th thoracic vertibrate, allowing the gases to be directed through the tube and into the lungs.
A primary objective of the treatment is the mechanical ventilation of the patient's lungs. This function normally induced by the patient's breathing, is typically impaired by the disease being treated. In order to create the air pressure necessary to artificially ventilate the lungs, the passageway around the tube has to be sealed. This is accomplished by an inflatable cuff provided around the tube. With the tube in place, the cuff is located about 3 to 5 centimeters above the carina and within the tube-like trachea.
The cuff is inflated to expand against the wall of the trachea and thereby to prevent gases that are being pumped into the lungs from simply backing up around the tube. This method of treatment has been quite successful for patients with chronic and acute respiratory disease. However, the method is not without complications.
Many entubated patients receiving the artificially induced ventilation may develop pneumonia. Pneumonia, which results from an infection of the lung may occur when pooled secretions, which have become infectious, are allowed, as a result of by-passing the upper airway, to enter the lungs. Unfortunately, this has been almost impossible to avoid with the prior endotracheal tubes.
The epiglottis is a form of valve that normally functions to selectively close the entry to the trachea and protect the airways (trachea and lungs) from secretions and particulate matter. The insertion of the endotracheal tube by-passes the protective system of the tracheo bronchial tree. Secretions that would normally be directed harmlessly through the digestive system follows the path of the tube, into the airway. The cuff above the carina provides a block to the downward flow of these secretions and are thus prevented from entering the lungs. The secretions become pooled above the cuff and if unattended, rapidly grow infectious bacteria that poses a serious risk to the patient.
The problem of these prior endotracheal tubes arises primarily upon cessation of the mechanical ventilation. The cuff is deflated in order to withdraw the endotracheal tube from the trachea. The infected fluid is now released to continue passage down the trachea and into the highly susceptible lungs where bronchitis or pneumonia develops rapidly. Whereas deflation of the cuff in the presence of the pooled secretions poses the greatest threat of lung infection, there is substantial risk also during treatment, i.e. with the cuff inflated. An incomplete seal caused by folds or creases in the cuff is not unusual. Whereas these folds or creases may not be a problem to the ventilation treatment it can allow microaspiration of the pooled secretions.